The present invention relates generally to gas turbine engines, and, more specifically, to turbine frames therein.
In a typical gas turbine engine, air is compressed in a compressor, mixed with fuel and ignited to produce combustion gases in a combustor, and channeled downstream through one or more stages of turbine nozzles and rotor blades. The blades extend radially outwardly from a disk which is joined to a shaft for powering the compressor or fan. The shaft is supported by bearings from a bearing support which forms part of a turbine frame.
An exemplary turbine frame disposed downstream of a last rotor stage, for example, includes a plurality of circumferentially spaced apart supporting struts which extend radially between outer and inner annular bands. The bearing support is fixedly joined to the inner band, and the outer band is fixedly joined to a structural casing of the engine.
Surrounding each of the struts is a hollow fairing which is suitably provided with pressurized cooling air bled from the compressor for cooling the turbine frame from the heating effects of the hot combustion gases which flow axially therethrough. The fairings are joined at their outer and inner ends to annular liners defining corresponding outer and inner flowpaths between which the combustion gases flow. During operation, the fairings are directly bathed in the combustion gases and therefore expand radially outwardly at a greater rate than the struts protected therein. The cooling air channeled through the fairings cools the fairings as well as the struts and further affects the differential thermal movement between the fairings and the struts.
In order to reduce thermally induced stress in the fairing assembly, it is mounted to float relative to the struts for obtaining unrestrained differential thermal expansion and contraction movement therebetween. Each fairing is suitably larger than the corresponding strut which it surrounds for receiving the cooling air for cooling these components during operation. In order to accurately axially and circumferentially position each fairing around its corresponding strut, axially spaced and independent supports or retainers are typically provided.
In one conventional design, mounting blocks having generally U-shaped recesses therein are mounted at various locations on the outer and inner liners so that the U-recess axially and circumferentially traps corresponding V-portions of the struts at their leading and trailing edges. For example, forward and aft U-blocks are mounted to the inner liner to trap the corresponding leading and trailing edges of the struts. Additional aft U-blocks are mounted to the outer liner to trap the trailing edges of the struts. And, a 360.degree. ring is attached to the outer liner adjacent the leading edges of the several struts to axially abut the outer band.
In this way, the ring and several U-blocks attached to the fairing assembly abut respective portions of the struts and outer band to accurately position the fairing assembly relative to the struts. During operation, aerodynamic loads imposed upon the fairing by the combustion gases are carried through the respective blocks and retaining ring into the strut assembly. Differential thermal expansion and contraction between the fairings and the struts is permitted without restraint from the struts by the mounting blocks and retainer ring which are allowed to slide freely in the radial direction subject only to sliding friction.
The multi-block and retainer ring configuration described above requires correspondingly configured parts for each location which increases the number of parts required therefor, with each of these parts typically having a different configuration for its different location relative to the struts. Furthermore, the several mounting blocks and retainer ring carry aerodynamic reaction forces caused by the aerodynamic force generated by the combustion gases on the fairings during operation, with the reaction forces necessarily being distributed among the mounting blocks and retainer rings. The distributed reaction loads correspondingly cause wear, and effect reaction moments or couples which increase the complexity of the structural design for accommodating the resulting stress within acceptable limits.